Known sensors are employed in order to measure the angular positions of rotating parts, for instance in the form of an engine shaft, absolutely over several revolutions. Their technical function is to be seen in that unlike sensors operating incrementally and with a counting action, they provide an output with the correct angle of rotation or angle position, respectively in every operational state, for instance after switching on or after interruption of operation.
An angle of rotation sensor of this type is described in the company publication IMAS (inductive modular absolute measuring system) of EUCRON, of Leinfelden-Echterdingen, Germany, which consists of coarse and fine angle-position sensor elements, which are coupled together in sequence by means of transmissions. Using a multiplexer, which is connected on the one hand with the sensor elements and on the other hand with processing electronic circuitry, the angular information of the individual sensor elements is sequentially processed. Driving the multiplexer and the furthermore the selection of an individual sensor element is performed by different DC levels, which is employed to modulate the sensor element excitation voltage, which is supplied to the multiplexer by the processing circuit. The multiplexer is made up of semiconductor components such as semiconductor switches for switching the sensor signals and comparators for detecting the DC control level. The auxiliary energy for driving the multiplexer is derived from the sensor element excitation voltage with the aid of rectifiers. The disadvantage of this angle of rotation sensor resides in the integration of semiconductor components at the point of measurement. Such components render the sensor sensitive to environmental effects such as interfering electrical and magnetic fields and furthermore extreme variations in temperature as are likely in drive technology.
A further angle-position sensor is described in German patent publication 3,734,938 A1. The arrangement provides a plurality of resolvers coupled by means of transmissions with one another. The transmission ratios are set at 2EXP(N). The code is a single step one or cyclic code, respectively. The linking of the angular information of the individual sensor elements is made by means of a redundant bit. The disadvantage of this arrangement is the limitation, due to the processing circuitry, to certain speed ratios. This is something which impairs optimization as regards design in the form of small units, which are an advantage. A further disadvantage is to be seen in the limitation to a single step code. Such code must be converted for processing in standard industrial control units by means of a code converter into the natural dual code. A further disadvantageous feature is the restriction, due to the processing circuit, to one single bit digit for linking the angular information of individual sensor elements. This limits tolerances for the transmission backlash of the transmissions to 1/4 revolution of the respectively preceding shaft. The mechanical complexity for the design of the transmissions is consequently higher than is necessary. A further disadvantage is the level of costs due to the exclusive use of resolvers.
A further sensor is disclosed in the German patent publication 3,246,959 C. In this case a plurality of sensor elements are coupled together in tandem using differential step down transmissions with small step down ratios. The disadvantage of the use of differential drives on the high speed input shafts is the high rotor speed of the following sensor elements coupled in sequence. This places high loads on the bearings thereof and leads to an expensive mechanical design.
Both the German patent publication 3,246,959 and also the German patent publication 3,734,938 disclose the sequential processing of the signals from the sensor elements with the aid of the multiplex method. However, there is no provision of a trouble-free multiplexer at little expense.
The German patent publication 2,907,672 discloses the employment of toroidal core chokes for the sequential processing the information bit of one or more angular encoders. Here it is a disadvantage that there is an extremely complex digital design of the angular encoders using magnetically encoding single elements and the low angular resolution, which can be attained.
Optical absolute angular sensors and furthermore capacitive angle of rotation sensors are disclosed in the German patent publications 2,938,318 C and 3,711,062 C. They utilize glass disks with optically encoded divisions or, respectively, stationary and rotating capacitor plates for encoding angular information. The disadvantage of the optical and capacitive sensors is their sensitivity to interfering electrical and magnetic fields and furthermore extreme temperature fluctuations owing to the integrated signal processing electronic system. A further disadvantage of the optical sensors is the sensitivity of the glass disks as regards vibrations and soiling.